GO学习笔记07

一、map

1.定义

 package main
    
    import "fmt"
    
    func main() {
        //map只有len,没有cap
        var m1 map[int]string
        fmt.Println("m1 = ", m1)
        fmt.Println("len = ", len(m1))
        fmt.Println("-----------")
    
        //make方式创建
        m2 := make(map[int]string)
        fmt.Println("m2 = ", m2)
        fmt.Println("len = ", len(m2))
        fmt.Println("-----------")
    
        //指定长度2
        m3 := make(map[int]string, 2)
        m3[1] = "java"
        m3[2] = "go"
        m3[3] = "python"
        fmt.Println("m3 = ", m3)
        fmt.Println("len = ", len(m3))
    
    }
    
    
    m1 =  map[]
    len =  0
    -----------
    m2 =  map[]
    len =  0
    -----------
    m3 =  map[1:java 2:go 3:python]
    len =  3

2.迭代

    package main
    
    import "fmt"
    
    func main() {
        m := map[int]string{1: "java", 2: "go", 3: "python"}
        for key, value := range m {
            fmt.Printf("key = %d, value = %s\n", key, value)
        }
    
        value, ok := m[0]
        if ok == true {
            fmt.Println("m[0] = ", value)
        } else {
            fmt.Println("不存在")
        }
        value1, ok1 := m[1]
        if ok1 == true {
            fmt.Println("m[0] = ", value1)
        } else {
            fmt.Println("不存在")
        }
    
    }
    
    key = 1, value = java
    key = 2, value = go
    key = 3, value = python
    不存在
    m[0] =  java

3.删除

m := map[int]string{1: "java", 2: "go", 3: "python"}
        for key, value := range m {
            fmt.Printf("key = %d, value = %s\n", key, value)
        }
    
        delete(m, 1)
        fmt.Println("m = ",m)
        
        key = 1, value = java
        key = 2, value = go
        key = 3, value = python
        m =  map[2:go 3:python]

4.作为参数传递

    import "fmt"
    
    func main() {
        m := map[int]string{1: "java", 2: "go", 3: "python"}
        test(m) //引用传递
        fmt.Println("m = ", m)
    }
    func test(m map[int]string) {
        delete(m, 1)
    }
    
    m =  map[2:go 3:python]

二、结构体

1.定义

 package main
    
    import "fmt"
    
    type Student struct {
        id int
        name string
        age int
    }
    
    func main() {
        //顺序初始化每个成员必须初始化
        var s1 Student = Student{1,"tony",18}
        fmt.Println("s1 = ",s1)
        
        //指定初始化，未初始化的参数默认为类型的默认值
        s2:=Student{name:"Tom",age:19}
        fmt.Println("s2 = ",s2)
    }
    
    
    s1 =  {1 tony 18}
    s2 =  {0 Tom 19}

2.指针类型的结构体

    package main
    
    import "fmt"
    
    type Student struct {
        id int
        name string
        age int
    }
    
    func main() {
        //顺序初始化每个成员必须初始化
        var p1 *Student = &Student{1,"tony",18}
        fmt.Println("p1 = ",p1)
    
        //指定初始化，未初始化的参数默认为类型的默认值
        p2:=&Student{name:"Tom",age:19}
        fmt.Println("p2 = ",p2)
    }
    
    p1 =  &{1 tony 18}
    p2 =  &{0 Tom 19}

3.结构体普通成员操作

    package main
    
    import "fmt"
    
    type Student struct {
       id   int
       name string
       age  int
    }
    
    func main() {
       var s Student
       s.id = 1
       s.name = "tony"
       s.age = 19
    
       fmt.Println("s = ", s)
    }
    
    s =  {1 tony 19}

4.结构体指针成员的操作

 package main
    
    import "fmt"
    
    type Student struct {
        id   int
        name string
        age  int
    }
    
    func main() {
        var s Student
        var p1 *Student
        p1 = &s
    
        //第一种
        p1.id = 1
        p1.name = "tony"
        p1.age = 19
        fmt.Println("p1 = ", p1)
        
        //第二种
        p2 := new(Student)
    
        p2.id = 2
        p2.age = 18
        p2.name = "tom"
        fmt.Println("p2 = ", p2)
    
    }
    
    p1 =  &{1 tony 19}
    p2 =  &{2 tom 18}

5.结构体的比较和赋值

    结构体和数组一样可以赋值和比较
    代码略

6.机构体作为函数参数01

    package main
    
    import "fmt"
    
    type Student struct {
        id   int
        name string
        age  int
    }
    
    func main() {
        s := Student{1, "tony", 18}
        test01(s)
        fmt.Println("main: ", s)
    
    }
    func test01(student Student) {
        student.id = 888
        fmt.Println("test01 = ", student)
    }
    
    
    test01 =  {888 tony 18}
    main:  {1 tony 18}

7.结构体作为函数参数02

    package main
    
    import "fmt"
    
    type Student struct {
        id   int
        name string
        age  int
    }
    
    func main() {
        s := Student{1, "tony", 18}
        test01(&s)
        fmt.Println("main: ", s)
    
    }
    func test01(p *Student) {
        p.id = 888
        fmt.Println("test01 = ", p)
    }
    
    
    test01 =  &{888 tony 18}
    main:  {888 tony 18}

8.可见性

 如果想使用别的包里面的函数、结构体类型、结构体成员
    函数名字、类型名、机构体成员变量名，首字母必须大写